Trifluoroethylene (CHF═CF2) is a known compound used as a monomer in the preparation of various fluorinated polymers. It has been used extensively in different markets (for example, in vinylidene fluoride copolymers) due to its ease of processing, chemical inertness and attractive ferroelectric, piezoelectric, pyroelectric and dielectric properties, see for instance Fluorinated Hydrocarbons—Advances in Research and Application: 2013 Edition. Q. Ashton Acton, PhD.—May 1, 2013. Scholarly Editions or Ferroelectric polymers: Chemistry, physics, and applications. Edited by Hari Singh Nalwa, Marcel Dekker, New York 1995.
Trifluoroethylene is a gas at ambient temperature. Trifluoroethylene is known to disproportionate with liberation of great amounts of heat resulting in a significant pressure rise and explosion and so the storage and transportation of trifluoroethylene poses a number of safety issues in view of its tendency to violently deflagrate, see for instance FEIRING A. E. et al Trifluoroethylene deflagration Chemical & Engineering News 1997 75 51 6
The disproportionation reaction can be triggered by the polymerization of trifluoroethylene which occurs spontaneously. For this reason polymerization inhibitors, such as limonene, are generally added in amounts of up to 5% by weight to trifluoroethylene. However polymerization inhibitors do not render trifluoroethylene stable, they only remove a potential source of ignition. Thus, the presence of known polymerization inhibitors is not sufficient to eliminate the deflagration hazard connected with the storage and transportation of trifluoroethylene (Halocarbon MSDS).
Although trifluoroethylene can be liquefied by sufficient pressurization in a container, storage and transportation of trifluoroethylene as a liquid is generally avoided because of the risks of explosion of the gas in equilibrium with the liquid (the gas phase may contain not enough polymerization inhibitor because the inhibitor is less volatile than trifluoroethylene). Thus, as a precaution, liquid trifluoroethylene is generally kept below −30° C. and its quantity is kept to the minimum required for the process. On the other hand a stable gas phase in equilibrium with a liquid phase would reduce the risk of ignition of the liquid phase itself, as deflagration of the liquid is usually possible only after ignition of the gas phase.
Studies with trifluoroethylene in the gas phase indicate that there is a reduced risk of disproportionation at pressures below 0.35 MPa. As pressure increases above this value, the risk of disproportionation and, consequently, deflagration increases. For this reason trifluoroethylene is generally stored, handled and transported at pressures not exceeding 0.30 MPa. The amount of trifluoroethylene transported per unit volume is thus very limited with a great impact on the cost of this material. The safety and consequently, cost issues related to the storage and transportation of trifluoroethylene are such to limit the use of trifluoroethylene as a monomer regardless of the potential economic interest of the polymers obtainable there from.
WO 2013/113785 discloses that certain compositions of trifluoroethylene and hydrogen chloride (HCl) are stable towards deflagration even when compressed to pressures above 0.35 MPa and thus they can be safely stored, handled and transported as a liquid or as a compressed gas at a pressure of up to 5.00 MPa. Although this appears to be a convenient process, for commercial scale production the handling of anhydrous hydrogen chloride raises other difficult safety related issues. Hydrogen chloride is a colorless, non-flammable but toxic and corrosive gas. Hydrogen chloride is typically stored as an anhydrous liquid at high pressure (vapor pressure is 35,000 mmHg at 25° C.). Hydrogen chloride is extremely soluble in water and the absorption of hydrogen chloride in water is strongly exothermic. Hydrogen chloride also reacts with many metals (including aluminum, zinc, calcium, magnesium, iron, tin and all of the alkali metals) to generate flammable hydrogen gas
Thus the need exist for means of safely storing and transporting trifluoroethylene without using any hazardous substance.